Orthopaedic surgeons must develop openings or cavities in long bones for a variety of reasons including fracture fixation and the implantation of stem based prostheses. Stems are used in prosthetic joint implants to anchor the prosthesis in a bone cavity. The bone receiving the stem is typically prepared by drilling a hole in the bone and creating an opening sized and contoured to receive the stem of the implant. The stem is inserted into a prepared cavity of a bone and a joint bearing surface attached or coupled to the stem, extends out to the cavity. An example of the preparation of a long bone for receipt of a femoral stem component of a total hip prosthesis is illustrated in U.S. Pat. No. 4,790,852 to Noiles which is hereby incorporated by reference.
When preparing a long bone for receipt of a stem, it is important to ream the bone to a suitable predetermined depth. Removal of more healthy bone than is necessary for implantation is always undesirable, and removal of too much or too little bone could result in an ill-fitted prosthesis. Orthopaedic surgeons use a variety of methods for indicating a predetermined reaming depth on a long bone reaming tool. Some surgeons simply mark the desired depth on the reamer with a pen so that the surgeon will know that the proper depth has been reached when the marking reaches the leading edge of the bone being reamed. This method has the disadvantage that markings can often be removed from the reamer by contact with body tissues or fluids during the reaming process.
Some orthopaedic instrumentation manufacturers have tried to improve depth markings on reamers by providing grooves transverse to the length of the reamer to provide a visual indicator to the surgeon similar to those made by pen. There are disadvantages to this approach as well. Transverse grooves may structurally weaken the reamer, shortening its useful life and possibly causing the reamer to fail during surgery. Additionally, the same reamer may be used to ream to a variety of different depths depending on the size of the stem being implanted. As a result, a large number of reamers each having a different depth marking must be maintained, resulting in an undesirable increase in instrument inventory. Alternatively, reamers must have multiple depth markings, which may result in confusion during reaming as to which is the correct depth mark.
Accordingly, it is an object of the present invention to provide a means for positively indicating a predetermined depth for a reamer while avoiding the aforementioned disadvantages.